TWO NEW SUNSPOTS: On Friday they didn’t exist. On Saturday they are big sunspots. Today, sunspots AR1726 and AR1727 are rapidly emerging in the sun’s northern hemisphere. The larger of the two, AR1726, contains nearly a dozen dark cores and spans 125,000 km from end to end. Click to view a 24-hour movie recorded by NASA’s Solar Dynamics Observatory:
AR1726 is the fastest-growing and, so far, the most active. It is crackling with C-class flares and seems capable of producing even stronger M-class eruptions. Because of the sunspot’s central location on the solar disk, any explosions this weekend will be Earth-directed.
STRONG SOLAR FLARE: The magnetic field of sunspot AR1719 erupted on April 11th at 0716 UT, producing an M6-class solar flare. NASA’s Solar Dynamics Observatory recorded the explosion’s extreme ultraviolet flash:
Shortly after the flare, a CME emerged from the blast site. NOAA forecasters estimate a 60% chance of geomagnetic storms on April 13th when the cloud reaches Earth. High-latitude sky watchers, be alert for auroras!
DOUBLE-BARRELED SUNSPOTS: Earth is staring down a double-barreled threat for solar flares–that is, sunspots AR1718 and AR1719. NASA’s Solar Dynamics Observatory photographed the pair during the early hours of April 10th:
Each of these sunspots has a ‘beta-gamma’ magnetic field that harbors energy for M-class flares. Of the two, AR1718 appears more likely to erupt. It is growing rapidly and is already crackling with lesser C-class flares. Any explosions today will be Earth-directed.
March 8, 2013: Using data from an aging NASA spacecraft, researchers have found signs of an energy source in the solar wind that has caught the attention of fusion researchers. NASA will be able to test the theory later this decade when it sends a new probe into the sun for a closer look.
The discovery was made by a group of astronomers trying to solve a decades-old mystery: What heats and accelerates the solar wind?
Solar wind flows away from the sun at speeds up to and exceeding 500 km/s (a million mph). More
The solar wind is a hot and fast flow of magnetized gas that streams away from the sun’s upper atmosphere. It is made of hydrogen and helium ions with a sprinkling of heavier elements. Researchers liken it to the steam from a pot of water boiling on a stove; the sun is literally boiling itself away.
“But,” says Adam Szabo of the NASA Goddard Space Flight Center, “solar wind does something that steam in your kitchen never does. As steam rises from a pot, it slows and cools. As solar wind leaves the sun, it accelerates, tripling in speed as it passes through the corona. Furthermore, something inside the solar wind continues to add heat even as it blows into the cold of space.”
Finding that “something” has been a goal of researchers for decades. In the 1970s and 80s, observations by two German/US Helios spacecraft set the stage for early theories, which usually included some mixture of plasma instabilities, magnetohydrodynamic waves, and turbulent heating. Narrowing down the possibilities was a challenge. The answer, it turns out, has been hiding in a dataset from one of NASA’s oldest active spacecraft, a solar probe named Wind.
Launched in 1994, Wind is so old that it uses magnetic tapes similar to old-fashioned 8-track tapes to record and play back its data. Equipped with heavy shielding and double-redundant systems to safeguard against failure, the spacecraft was built to last; at least one researcher at NASA calls it the “Battlestar Gallactica” of the heliophysics fleet. Wind has survived almost two complete solar cycles and innumerable solar flares.
“After all these years, Wind is still sending us excellent data,” says Szabo, the mission’s project scientist, “and it still has 60 years’ worth of fuel left in its tanks.”
An artist’s concept of the Wind spacecraft sampling the solar wind. Justin Kasper’s science result is inset.
Using Wind to unravel the mystery was, to Justin Kasper of the Harvard-Smithsonian Center for Astrophysics, a “no brainer.” He and his team processed the spacecraft’s entire 19-year record of solar wind temperatures, magnetic field and energy readings and …
“I think we found it,” he says. “The source of the heating in the solar wind is ion cyclotron waves.”
Ion cyclotron waves are made of protons that circle in wavelike-rhythms around the sun’s magnetic field. According to a theory developed by Phil Isenberg (University of New Hampshire) and expanded by Vitaly Galinsky and Valentin Shevchenko (UC San Diego), ion cyclotron waves emanate from the sun; coursing through the solar wind, they heat the gas to millions of degrees and accelerate its flow to millions of miles per hour. Kasper’s findings confirm that ion cyclotron waves are indeed active, at least in the vicinity of Earth where the Wind probe operates.
Ion cyclotron waves can do much more than heat and accelerate the solar wind, notes Kasper. “They also account for some of the wind’s very strange properties.”
The solar wind is not like wind on Earth. Here on Earth, atmospheric winds carry nitrogen, oxygen, water vapor along together; all species move with the same speed and they have the same temperature. The solar wind, however, is much stranger. Chemical elements of the solar wind such as hydrogen, helium, and heavier ions, blow at different speeds; they have different temperatures; and, strangest of all, the temperatures change with direction.
“We have long wondered why heavier elements in the solar wind move faster and have higher temperatures than the lighter elements,” says Kasper. “This is completely counterintuitive.”
The ion cyclotron theory explains it: Heavy ions resonate well with ion cyclotron waves. Compared to their lighter counterparts, they gain more energy and heat as they surf.
An artist’s concept of Solar Probe Plus approaching the sun where it can test the ion cyclotron theory. More
The behavior of heavy ions in the solar wind is what intrigues fusion researchers. Kasper explains: “When you look at fusion reactors on Earth, one of the big challenges is contamination. Heavy ions that sputter off the metal walls of the fusion chamber get into the plasma where the fusion takes place. Heavy ions radiate heat. This can cool the plasma so much that it shuts down the fusion reaction.”
Ion cyclotron waves of the type Kasper has found in the solar wind might provide a way to reverse this process. Theoretically, they could be used to heat and/or remove the heavy ions, restoring thermal balance to the fusing plasma.
“I have been invited to several fusion conferences to talk about our work with the solar wind,” he says.
The next step, agree Kasper and Szabo, is to find out if ion cyclotron waves work the same way deep inside the sun’s atmosphere where the solar wind begins its journey. To find out, NASA is planning to send a spacecraft into the sun itself.
Solar Probe Plus, scheduled for launch in 2018, will plunge so far into the sun’s atmosphere that the sun will appear as much as 23 times wider than it does in the skies of Earth. At closest approach, about 7 million km from the sun’s surface, Solar Probe Plus must withstand temperatures greater than 1400 deg. C and survive blasts of radiation at levels not experienced by any previous spacecraft. The mission’s goal is to sample the sun’s plasma and magnetic field at the very source of the solar wind.
“With Solar Probe Plus we’ll be able to conduct specific tests of the ion cyclotron theory using sensors far more advanced than the ones on the Wind spacecraft,” says Kasper. “This should give us a much deeper understanding of the solar wind’s energy source.”
March 1, 2013: Something unexpected is happening on the sun. 2013 is supposed to be the year of Solar Max, the peak of the 11-year sunspot cycle. Yet 2013 has arrived and solar activity is relatively low. Sunspot numbers are well below their values in 2011, and strong solar flares have been infrequent for many months.
The quiet has led some observers to wonder if forecasters missed the mark. Solar physicist Dean Pesnell of the Goddard Space Flight Center has a different explanation:
“This is solar maximum,” he suggests. “But it looks different from what we expected because it is double peaked.”
A new ScienceCast video explores the puzzling behavior of ongoing Solar Cycle 24. Play it
Conventional wisdom holds that solar activity swings back and forth like a simple pendulum. At one end of the cycle, there is a quiet time with few sunspots and flares. At the other end, Solar Max brings high sunspot numbers and solar storms. It’s a regular rhythm that repeats every 11 years.
Reality, however, is more complicated. Astronomers have been counting sunspots for centuries, and they have seen that the solar cycle is not perfectly regular. For one thing, the back-and-forth swing in sunspot counts can take anywhere from 10 to 13 years to complete; also, the amplitude of the cycle varies. Some solar maxima are very weak, others very strong.
Pesnell notes yet another complication: “The last two solar maxima, around 1989 and 2001, had not one but two peaks.” Solar activity went up, dipped, then resumed, performing a mini-cycle that lasted about two years.
The same thing could be happening now. Sunspot counts jumped in 2011, dipped in 2012, and Pesnell expects them to rebound again in 2013: “I am comfortable in saying that another peak will happen in 2013 and possibly last into 2014,” he predicts.
Another curiosity of the solar cycle is that the sun’s hemispheres do not always peak at the same time. In the current cycle, the south has been lagging behind the north. The second peak, if it occurs, will likely feature the southern hemisphere playing catch-up, with a surge in activity south of the sun’s equator.
Recent sunspot counts fall short of predictions. Credit: Dr. Tony Philips & NOAA/SWPC [full plot]
Pesnell is a leading member of the NOAA/NASA Solar Cycle Prediction Panel, a blue-ribbon group of solar physicists who assembled in 2006 and 2008 to forecast the next Solar Max. At the time, the sun was experiencing its deepest minimum in nearly a hundred years. Sunspot numbers were pegged near zero and x-ray flare activity flat-lined for months at a time. Recognizing that deep minima are often followed by weak maxima, and pulling together many other threads of predictive evidence, the panel issued this statement:
“The Solar Cycle 24 Prediction Panel has reached a consensus. The panel has decided that the next solar cycle (Cycle 24) will be below average in intensity, with a maximum sunspot number of 90. Given the date of solar minimum and the predicted maximum intensity, solar maximum is now expected to occur in May 2013. Note, this is not a unanimous decision, but a supermajority of the panel did agree.”
Given the tepid state of solar activity in Feb. 2013, a maximum in May now seems unlikely.
“We may be seeing what happens when you predict a single amplitude and the Sun responds with a double peak,” comments Pesnell.
Incidentally, Pesnell notes a similarity between Solar Cycle 24, underway now, and Solar Cycle 14, which had a double-peak during the first decade of the 20th century. If the two cycles are in fact twins, “it would mean one peak in late 2013 and another in 2015.”
No one knows for sure what the sun will do next. It seems likely, though, that the end of 2013 could be a lot livelier than the beginning.
Author: Dr. Tony Phillips
FARSIDE HOTSPOT: As big sunspot AR1678 departs, another active region is approaching. NASA’s STEREO-B probe, stationed over the farside of the sun, is monitoring a significant ultraviolet hotspot. It is circled in this 360-degree Stoneyhurst projection of the entire solar surface:
In the projection, longitudes between +90 and -90 degrees are on the Earthside of the sun; other longitudes are on the farside. The image shows that the farside active region is poised to rotate from farside to Earthside within the next couple of days. Perhaps it will bring some flares with it.
FILAMENT ERUPTION: Solar activity is low, but not zero. During the early hours of Feb. 13th, a magnetic filament erupted near the sun’s SW limb. NASA’s Solar Dynamics Observatory recorded the blast (click to set the scene in motion):
The extreme UV movie shows the filament flinging itself into space followed by the formation of a “canyon of fire” marking the channel formerly occupied by the filament. The glowing walls of the canyon are formed in a process closely related to that of arcade loops, which appear after many solar flares.
As erupting magnetic filaments often do, this one launched a coronal mass ejection (CME) into space. NASA’s STEREO-A spacecraft spotted the expanding cloud, which does not appear to be heading for Earth or any other planet.
CHANCE OF FLARES: So far today, solar activity is low. However, that could be the calm before the storm. The magnetic field of big sunspot AR1654 has grown more complex. It is now classified as a ‘beta-gamma-delta’ magnetic field, which means it harbors energy for X-class eruptions. Solar flare alerts:text, voice.
If there is a flare today, the blast would be Earth-directed. This sunrise shot, taken at dawn on Jan. 16th by Jan Koeman on the bank of the Westerschelde River in the Netherlands, shows how AR1654 (circled) is almost directly facing our planet:
“Sunspot complex AR1654-AR1656 was clearly visible through the clouds and mist,” says Koeman. “It was a wonderful sunrise even at -8 degrees celsius.”
VERY SPOTTED SUN: Solar activity is still relatively low, but the appearance of the sun suggests the quiet might not last. Over the weekend, a profusion of new sunspot groups peppered the solar disk with dark cores–each one a potential source of eruptions. NOAA forecasters estimate a 35% chance of M-class flares and a 5% chance of X-flares during the next 24 hours. Solar flare alerts:text, voice.
There are so many spots on the sun, even a jumbo jet cannot hide them:
Raffaello Lena took the picture on January 5 not far from the international airport in Rome, Italy. “An animation of the flyby is available here,” he says.
GEOMAGNETIC STORM WATCH: A geomagnetic storm is brewing around Earth’s poles following a CME strike on Nov. 23rd. A second CME is en route, due to arrive on Nov. 24th. NOAA forecasters say there is a 65% chance that the second strike will trigger strong storms at high latitudes.
